With rapid development of ultrasonic imaging technology, an ultrasonic imaging device could collect abundant high and low echo signals with increasing signal dynamic range. However, due to attenuation, non-uniform beam and probe directivity, the morphology of ultrasonic signals and noises appeared on an image are incongruous. The dynamic range of the signals may be varied at different positions times. Hence, a plurality of methods within relative fields has been proposed so as to display low and high echo signals simultaneously with more detail signals.
The main idea of these methods has been implemented by determining a signal dynamic range by noise signals and mapping ultrasonic signals based on the determined signal dynamic range. One of the disadvantages of these methods is that the determination of the noise signals is difficult, especially distinguishing useful tissue information from noise for relatively weak ultrasonic echo signals. With an ineffective result of distinguishing, weak signals or noises could not be controlled efficiently. Another drawback of these methods is unnatural image local contrast produced by simply mapping. Excessive stretching performed on a region having an actually small dynamic range may lead to excess black holes on tissues or highlighted lumen speckle noises.
A method for distinguishing tissue from noise has been also disclosed; however, this method fails to significantly enhance weak signals because of lacking of scalable operation on the image. In addition, such method requires an image having better contrast and resolution to be a basic image, resulting in burdening image processing and increasing processing difficulty.